Method of making porous material



Oct. 27, 1942. R. P. KOEHRING METHOD OF MAKING POROUS MATERIAL Filed March 27, 1940 INVENTOR .5: Hula/7a Patented on. 2?, rear:

METHOD OF MAKING POROUS MATERIAL Roland P. Koehring, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a

corporation oi! Delaware Application March 27, 1940, Serial No. 326,220

6 Claims.

This invention relates to a method for making highly porous metal articles and is particularly concerned with the method of making porous metal articles having varying porosity through the cross section thereof.

It is an object of the invention to provide a method for forming porous metal sheet material of varying porosity throughout the cross-section thereof by the aid of gravity whereby metal powder particles of varying grain size may be deposited upon a supporting surface in accordance with their grain size by the use of fluid agitation or gravity deposition.

In carrying out the above object, it is a further object to agitate metal particles of varying grain size by means of air or liquid, whereby upon cessation of the agitation, the particles settle upon a supporting surface in the order of their mass.

A still further object is to provide a method for depositing metal particles in accordance with their mass upon a supporting surface by means of first depositing the particles of metal powder against a screen spaced a substantial distance from a supporting plate by means of a fluid stream and then, upon cessation of the stream of fluid, which is holding the particles against the screen, permitting gravity deposition of the particles upon the supporting plate in the order of their mass.

It is another object of the invention to provide apparatus for carrying out the methods heretofore set forth.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing wherein preferred embodiments of the present invention are clearly shown.

In the drawing:

Fig. 1 diagrammatically illustrates an apparatus which may be used to deposit metal particles upon a supporting plate in the order of their mass.

Fig. 2 is a view showing another type of apparatus for accomplishing the same purpose.

Fig. 3 shows still another type of apparatus for depositing metal particles in the order of their mass upon a supporting plate.

Fig. 4 shows a diagrammatic view of an apparatus wherein powder metal particles may be deposited in the order of their mass by means of a liquid, and, Fig. 5 is an enlarged fragmentary sectional view showing the powder metal particles deposited upon a supporting plate in accordance with their mass.

This invention is directed to a method for making porous metal articles as disclosed in application Serial No. 326,235, now matured into Pat. No. 2,267,918, granted Dec. 30, 1941, assigned to the assignee of the present invention. In this application an article is made which comprises a thin layer of porous metal having a graduated porosity that is to say, having a varying porosity through the sheet wherein difierent strata of different porosities are present. In the present invention, the method is disclosed whereby the mtal particles may be deposited upon a support prior to the sintering thereof in accordance with their mass, that is to say, the coarser metal particles may be deposited prior to deposition of the smaller metal particles whereby the porosity of the finished article will vary through the crosssection thereof.

I accomplish the selective deposition of metal powder particles by the use of fluid agitation and gravity settling. The drawing illustrates various forms of apparatus which may be used to carry out the invention. Referring more specifically to Fig. 1, 20 designates an elongated, vertical chamber WhlCh encloses a support or plate 22 supported upon suitable brackets 24 adjacent the lower portion of the chamber 20. The plate 22 may be made from numerous materials in accordance with the specific type of porous metal which is contemplated. If a porous metal sheet is desired the plate :2 may be made from any non-adhering material winch will not melt at the temperatures of sintering, for example, graphite is a suitable material, or the plate may be steel, which has dusted over the surrace thereof a layer of alundum or some other refractory material, or the plate may be maue ll'ulIl a refractory material, such as alundum. Also the plate may be a chrome steel WIllCIl has a surface thereof oxidized so that the metal powder will not adhere thereto upon heating, or the plate may be steel having an oxidized chrome plated surface. If it is desired to bond the porous metal layer to the plate, any of the conventional materials may be utilized, copper, nickel, steel, copper plated steel, iron, etc.

The powder is introduced into the chamber 20 through a funnel 26 which is at the end oi a tube 28. The powder charge is placed in the funnel 26 and then compressed air or any other type 01 gas is blown through the tube 28 to agitate the powder upwardly in the chamber 20. The air pressure is then turned all and the powder is permitted to settled by means of gravity upon the plate 22. It is apparent, that the powder will settle in accordance (with Stokes law) with its mass, so that the larger articles of metal powder will settle first upon plate 22, such particles being designated at 30, Fig. 5, and the smaller metal particles 32 will settlevupon the top of the particles 30.

In Fig. 2 a modification is illustrated wherein the powder is introduced through tube 34 at the bottom of a chamber 26 and the powder is blown upwardly in the chamber 38 around plate 22 and through apertured brackets 38. The top of chamber 38 is open and has placed therein adjacent the top thereof, a screen 40 which has a smaller mesh size than the grain size of the metal particles being blown into the chamber. In this manner, the metal powder is deposited against the screen, as long as the airpressure in pipe 34 is maintained. As soon as the air pressure is stopped, the powder deposited against the screen it falls therefrom, due to gravity and settles upon the plate 22 in the order of its mass.

Fig. 3 shows another modification wherein the powder is introduced into the chamber through a Jet 42 by means of mixing the powder with the air, in this instance, the powder is first placed in a funnel 44 disposed exteriorly of the chamber and is mixed with the air stream prior to its introduction into the chamber.

Fig. 4 shows still another means of obtaining the desired settling eifect upon plate 22. In this instance the powder is held in a hopper 46, adjacent the top of a chamber 48 which includes the plate 22 supported upon suitable brackets 50. The chamber 8 includes a drain valve 52 at the bottom thereof and is substantially filled with a liquid which may be selected from a number of classes, such as water, organic compounds, etc. I prefer selecting the liquid from the organic class which includes gasoline, benzene, acetone, toluene, xylene and other organic liquids which are readily evaporated. The powder is mixed with the liquid and may be agitated in the chamber and then may be permitted to settle through the liquid. In this manner, the mass of the particles determines their rate of settling through the liquid upon the plate 22. After the layer of powder has settled on plate 22, the liquid may be 'drained off gradually through valve 52 andthe plate with the powder metal layer thereon may be removed, after which an evaporation of the remaining fluid may be accomplished in the air or by gentle heating.

The plate with the metal powder layer thereon, after being removed from the chambers in any of the embodiments shown in the drawing, is then placed in a sintering furnace and heated under non-oxidizing conditions for a time and for a temperature sufficient to cause the metal powder particles to sinter together into a porous metal sheet which has varying degrees of porosity throughout the cross-section thereof.

For illustrative purposes only, the following example is given to clarify the sintering procedure. Bronze particles of varying grain size, for example, from 80 to 300 mesh, are deposited by means of gravity upon a graphite plate, this layer upon the plate is then placed in a sintering furnace and heated at a temperature in the neighborhood from 1500 to 1800 F. for a time of from to minutes under non-oxidizing conditions. After cooling under suitable conditions, the plate is removed from the furnace and the porous metal layer may be lifted therefrom.

In all of the embodiments, pre-alloyed particles of metal powder are preferably used since, if mixtures ofmetalpowdersareuseithesettling rate will be difierent, due to the difference in density of various materials. For this reason, it is preferable to attach the constituent metals to one another prior to the gravity, settling operation if combinations of metals are to be used. It is apparent, that single metal powders may be utilized for example, copper powder, nickel powder, aluminunmpowder, in which case, the sintering temperature should be slightly below the melting point of the metal powder. If mixtures of metal powders are utilized, the sintering temperatures should be intermediate the melting points of the metal powder used for example, the mixtures of tin-copper, tin-nickel, copper-nickel, copper-iron etc., may all be used satisfactorily and in each case it is'preferred that the two constituents are pre-alloyed to some extent prior to the operation, that is tosay, in the instance of copper-tin, for example, the tin powder should be deposited on the surface of the copper particles and should be alloyed thereto to some degree. It is not necessary,and in fact, it is preferable that the degree of alloying is not complete since this aids in sintering the metal particles together and in accomplishing a stronger bond and a uniform porosity. Pre-alloyed metal powders and articles made therefrom are disclosed in copending application Serial No. 322,753, assigned to the assignee of the present invention.

In some cases, it may be desirable to form a porous metal layer upon a steel or other solid metal back, such as is disclosed in my copending Patent No. 2,198,253. In this instance the gravity deposit may be carried out directly on a sheet of steel or other metal previously disclosed, in which case, the sintering is carried out under the same conditions as previously noted for providing a finished article which comprises a porous metal layer of changing porosity throughout the crosssection thereof which is bonded directly to the surface of the metal supporting element. Such articles are suitable for use as bearings, clutches, etc.

Porous metal plates as made by the method disclosed herein have many uses, such as, filters and fluid flow metering devices and the like. Other methods of making these articles are disclosed in application Serial No. 326,236, assigned to the assignee of this invention.

While the embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. The method of making porous metal sheet material wherein the porosity at one side of the sheet is different than the porosity of the other side of the sheet comprising the steps of, agitating metal powder of varying grain size by means of a fluid in a large chamber, causing said metal powder to settle upon a supporting surface solely bygravity, in accordance with the mass of the particles of varying grain size, and then sintering the settled powder upon said supporting surface under suitable conditions and for a time and at a temperature suflicient to cause the particles of powder to bond together and form a porous metal sheet of high porosity wherein the porosity at one side of the sheet is diiferent than the porosity of the other side of the sheet.

2. The method as defined in claim 1, wherein the is al 3. The method disclosed as defined in claim 1, wherein the fluid used for agitating the metal powder is a volatile non-oxidizing organic liquid.

4. The method for forming porous metal sheet material having a varying porosity from one side of the sheet to the other comprising the steps of, providing a chamber closed at the top portion thereof by means of a'screen, placing a plate 01' graphite or the like adjacent the lower portion of said chamber, blowing metal powder of varying particle size into the said chamber at a point remote from said screen for agitating the metal powder and blowing the same against said screen, stopping the air flow whereby the fluid used for agitating the metal powder r.

' metal powder on the screen drops downwardly with the aid of gravity upon said plate whereby the larger metal particles due to their mass settle upon the plate prior to the settling of the smaller metal particlesfor forming a layer of powder metal 01 graduated porosity, removing the plate with the metal powders thereon, and heating the same under suitable conditions for a time and for a temperature suflicient to cause the metal particles to sinter together into a strong highly porous sheet having a varying porosity from one side thereof to the other and then removing the sheet from the plate.

5. The method of making porous metal sheet material wherein the porosity through the sheet is different in different strata thereof, the steps of agitating metal particles of varying grain size by means of a fluid, settling the particles by means of gravity upon a supporting plate, and then sintering the powdered metal layer under suitable conditions for forming a porous metal sheet having varying porosity through the crosssection thereof.

6. A method as defined in claim 5 wherein the porous metal layer is bonded in situ to the supporting plate during the sintering step.

ROLAND P. KOEHRING. 

